The present invention generally relates to a method for producing textured composite articles. More particularly, this invention relates to a method by which a textured surface is produced on a composite article through the use of a textured interfacial layer that is applied to the mold in which the article is subsequently formed, and wherein the textured interfacial layer is retained on the article surface after the molding operation as a removable protective coating that when removed exposes the textured surface of the article.
Open tool molding is a process for producing relatively low-cost composite panels at low volumes. While steel molds are often used for other molding operations, the open tool molding process was developed to use less expensive one-sided epoxy or polyester molds to produce various products, such as recreational vehicle (RV) composite panels with an in-mold finish. In this process, the mold surface is cleaned and waxed, after which a layer of gel coat is applied and then partially cured. A laminate is then applied to the gel coat layer, and the laminate and gel coat are cured to form a unitary part having a surface that is defined by the cured gel coat. Molded parts can be produced by this method to have a class A finish bearing any desired color originally carried by the gel coat.
While the use of a low-cost epoxy or polyester mold offers significant cost advantages over other molding methods used to produce composite articles, there are certain limitations imposed by a polymeric mold. One such example is the molding of panels, such as automotive interior panels, for which a textured finish is desired. In the past, plastic textured panels have been made by either injection molding or compression molding using steel molds. A grained profile is formed on the surface of the steel mold during the tool making process. The grained surface profile is then transferred onto the surface of the molded parts, creating a textured surface finish. Because of the hardness of the steel molds, the grained surfaces maintain their appearance for many years of production. In contrast, polymeric molds do not have the same level of hardness and, therefore, a grained surface created on a polymeric mold wears out quickly. The vertical walls of a grained polymeric mold are particularly vulnerable to wear during demolding, with the result that an uneven surface finish is produced after molding only a few parts. Consequently, polymeric open tool molds have been generally limited to molding articles with smooth, glossy surfaces.
In view of the above, it would be desirable if a method were available for producing composite articles with a textured finish using a low-cost polymeric mold whose mold surfaces are not damaged by the molding operation.
The present invention is directed to a molding process that uses an interfacial layer to isolate the surface of the mold from the surface of a composite article produced with the mold. According to the invention, a solution can be deposited on the mold surface to form the interfacial layer, whose surface opposite the mold surface is textured. The texture of the interfacial layer is then transferred to the surface of the composite article produced with the mold. After demolding, the interfacial layer is removed from the article to expose an underlying textured surface of the article.
A suitable molding process of the present invention generally entails spraying a polymeric solution on an untextured mold surface of a mold so that the polymeric solution forms the textured interfacial layer of this invention. According to the invention, certain spray techniques are capable of depositing a polymeric solution to produce an interfacial layer whose outer surface texture can be controlled by the spray parameters, such as pressure and spray gun orifice size. A composite material is then deposited on the textured interfacial layer so that the composite material contacts the textured interfacial layer and has a surface that is textured by the interfacial layer. The composite material and the textured interfacial layer are then cured so that the composite material forms a composite article having a textured surface, and so that the textured interfacial layer clings to the textured article surface. The textured interfacial layer can then be immediately removed from the composite article, or left on the article as a temporary protective coating during shipping and handling and then later removed prior to or after the article is installed or assembled with other components.
In view of the above, a significant advantage of this invention is that an open tool mold can be fabricated to have smooth mold surfaces, with the interfacial layer being the sole means for producing a textured surface on an article produced with the mold. As a result, molds formed from lower cost and less durable materials, particularly polymers such as epoxies and polyesters, can be used to produce articles with textured surfaces, without quickly damaging or wearing out the mold surfaces.
Other objects and advantages of this invention will be better appreciated from the following detailed description.